Ball or pebble mill



Patented .lune 9, l925 ternana cil-mantas n. onstaan, or nrvnnsnon, oanrronfnra..

' nant on Panni-,n unitn Application led February 23, 1921i. Serial No. warned.

To all wlw/m, t may concern.'

` Beit known that 1, CHARLES L. CARMAN, a citizen of the United States, residing at Riverside, in the county of Riverside, State of California, have invented a. new and useful linprovement in Ball or Pebble Mills, of which the following is a specification.

rlhis invention relates to crushing or grinding mills of the type wherein the material to be reduced to a state of fine division is subjected to the action of crushing or grinding bodies contained in a rotary member formed for example as a tube or barrel. This invention is particularly intended for use in connection with tube mills in which the said enclosing body is formed as a tube rotating on a substantially horizontal axis and provided at.one end with means for feed of the material and 'at the other end with means for discharge of the ground or reduced material. The main object of the presentinvention is to improve the operation of tube mills by providing for automatic classicati'on according to the size of the grinding bodies or media longitudinally of the mill so as to provide for maximum efliciency in crushing and grinding An important object of the present invention is to improve the crushing and grindin'g action in tube mills by providing for automatic classification of the grinding bodies or media according to their size longitudinally in the mill in such manner that the larger grinding bodies will be presented near the feed end ofthe mill and the size i vof the grinding bodies will diminish progressively from the feed end toward the discharge end.

A further object of the invention is to provide for such classification of the grinding bodies of the media while preserving the proper ratio of the amount of grinding media to the amount of material being oper- ,ated upon throughout the length of the mill.

Another object of the invention is to provide in a-tube mill for classification of the crushing or grinding media longitudinally in the mill While providing for most eHeative operation of thepsaid media throughout the length of the mill.

Another object of the invention is to pro vide for tube mills a lining which is designed to accomplish the above results and which can readily be removed and replaced., l

Ytion is not limited to such a construction, as it may be of somewhat larger diameter at the feed end or at the discharge end as may be found desirable in any particular case, Sald tubular body 1 is provided with a head 2 at one end having a hollow trunnion 3 mounted to turn in the bearing 4 on a standard 5 and at the other end the tubular member 1 is provided with a head 6 having a hollow trunnion 7 mounted to turn in a bearing 8 on a standard 9. Suitable means indicated at 10 are provided for feeding material through the hollow trunnion 3 at the feed end of the mill and suitable means such .as perforated plate 11 and radial flights 12 are provided for controlling the discharge of crushed and ground material to the outlet 13 of the mill consisting of the bore in the hollow trunnion 7,' The tubular casing 1 is provided with suitable means for rotation thereof in the mills,l that is to say, on a substantially horizontal axis; for example the head member 6 may beprovided with a gear wheel 14C operated by a pinion 15 on a shaftl which is provided with pulleys 17 or other drive means. The inner vwall of the tubular memloer 1 is formed or provided with a series of annular sections or portions each comprising an inclined face 18 and an abrupt face or shoulder 19, said inclined face being formed as a frusto-conioal face which flares.

or inclines outwardly toward the feed end of the machine. The abrupt faces 19 are shown as extending perpendicular to the longitudinal axis of thel mill but it will be understood that these faces are not necessarily perpendicular to such axis but may be somewhat inclined thereto, provided that they are more abrupt or have a greater inclination to the longitudinal axis of the machine than the inclination of the face 18. For convenience in construction, installation and repair I prefer to make these sections of the tubular mill wall as separate rings forming removable lining sections y20 supported within the tubular member 1 in any usual manner of tubey suitable manner so as to be rigidly mounted therein, said sections being constructed for example of a hard cast iron or of hard steel or'of any other suitable material. In prac tice the edges of the abrupt faces 19 may be rounded but in any case such rounding would naturally result from theat-trition of the material after a short period of operation.

The incline of the faces 18'- may, as indi-` cated in the drawing, be about 30 relative to the longitudinal axis of the machine or it may be less or more than that amount according to the amount of-classifying action desired. A. cylindrical ring 2l may be provided between the conical ring sections 20 and the perforated discharge plate 12. It is not essential to the invention that the inclined and abrupt .portions be contiguous, as flattened or cylindrical wall portions may be provided at either end of the respective inclined portions. i

rlhe operation of the mill is as follows:

A suitable number of balls, pebbles or other crushing and grinding bodies are placed within the mill body and for most effective results l prefer that such crushing and grinding bodies be of different size. lt will be understood however that even if thesaid bodies are of the same size origient size by the operation of the mill as such bodies are worn away and other ones are supplied from time to time to replace the same. The material to be crushed or ground is supplied to the feed means 10 in any suitable manner and is thereby fed to the interior of the tubular borj; l. This operation' proceeds in the usual manner of a tube mill, except that by reason of the conical or inclined surfaces presented by the lining sections 20 there is a classifying `e'ect on the balls, pebbles or crushing and grinding bodies whereby the larger balls, etc., are caused to arrange themselves nearer the feed end and the size of the balls, pebbles, etc., decreases progressively towards the `discharge end. As a result of such a classification of the balls, pebbles, or grinding bodies according to size,'the crushing and grinding action is performed with more effectiveness both as to power consumed and as to output for a given installation. In the o eration of a tube mill, it has been found t at the work is almost entirely' do-ne by percussion, or impact, rather than b attrltion. The cylinder is rotated at suc a pe'-v ripheral speed as to producef the greatest average fall of the ball mass, the work being done by the balls striking against the lining` on the down going portion ofthe mill, near the bottom, and crushing the mate-rial being ground,V by each individual ball striking on some individual article, exactly as a hammer would crush 1t on an anvil. As a matter 'of fact the balls are active hammers rand the lining of the mill is an anvil, between which the material in the interstices of the ball mass is finally crushed to the desired fineness.

It is also well established `by practice that the balls should be of a size just large enough to crush the particle of material with which it comes in contact. Alarger ball would do'the work, but there can not be as great a number of large as small balls in the mill, and as a consequence, the large balls do not produce as great a quantity of very line material as do the same volume of small balls. 0n the other hand, the small balls have-very little e'ect on large particles of material. Therefore in order to secure economical results, it is the present practice to do the grinding in steps, grading the balls to the work as the material is` reduced in size. For this reason thelarge balls are placed in the preliminary mills, called ball mills and the small balls in the tube mills,

where the finishing is done.

While I do not wish to limit myself to any theory of operation of the conical or inclinedlining sections in effecting the classification above referred to, it may be stated that the effect o-f such inclines of the lining sections is to cause rebound of the balls fallnally they will eventually become of dierf due to sliding of the balls on the inclined surfaces of the lining sections, such sliding action bein more pronounced in the case of' the larger alls on account of the greater frictional resistance obstructing the movement of the smaller balls by reason of their larger ratio of surface in ro-portion to mass. In further explanation o the classifying action it may be stated that every ball in the mill willtravel'ina path exactly in a plane at right angles to the axis of rotation, unless acted upon by some extraneous force. No force can act upon the ball while it is resting in the mass aga-inst the shell, as there is no mass movement .relatively between its various units, 'nor between the mass and the shell, except that of the rotative effect of the mill in raising the mass to a pointin the circumference where gravity overcomes thc centrifugal force of the rotation, and the balls start off on the trajectory of their own to the lowest point against the lining. This action does not classify the balls if the lining is cylindrical, but, if it is conical, the impact of the balls against the inclined surfacel causes them to `rebound more or less on the an le of reaction, depending upon the resiliency of the materials of the balls and lining. The direction of the rebound will be toward the large end of the cone. This migrate to one end` of the mill, but at this point another factor enters into the action.

the preponderance of the greater balland in addition, diverts the larger ball in a proportional degree toward the larger end of the conical lining, therefore the largest balls get to one end o-f the mill, the next in size arrange themselves alongside of them, and so o-n down to thel other end where the smallest balls will be found. Such an arrangement of the balls is ideal, for the number of the balls should increase in the same ratio as does the number of the particles of the material in its progress through the mill. As the larger balls wear down they automatically arrange themselves according to their size until worn out. y The above described const cion, in which the diameter of the mill 1s substan-Y tially the same for the entire length thereof, enables a maximum fall of the crushing bodies to be maintained throughout the length of the mill and thereby ensures the exertion of maximum crushing force on the small particles by the small balls, as well as on the larger particles by the larger balls. This is a distinct advantage over mills of the cone type, in which the fall of the crushing bodies continually decreases toward the discharge end.

What I claim is:

l. A tube mill comprising a tubular body having its inner wall formed with a plurality of abrupt shoulders with intervening frusto-'conical portions flaring toward the feed end of the mill, said tubular mill body being provided with means for feeding material to one end thereof, and means for discharging material from the other end thereof.

' 2. A tubular mill body provided with means for feeding material into one end thereof and means for discharging material from the other end thereof, said mill body having a lining composed of ring sections,

each ring section having a frusto-conical face portion flarin toward the feed end of the mill body an an abrupt shoulder at the smaller diameter end of said face.

3. AAv mill substantially cylindrical 1n shape, and formed with a plurality of wall portions on the inner wall -of the mill, said wall portions being inclined outwardly L from the axis of the mill toward the feed end thereof, and with a plurality of wall portionsisubstantially perpendicular to the axis of the mill and between said inclined wall portions, lsaid mill being provided with a plurality of crushing bodies and with means :for rotating the mil 4., A tube mill comprising a substantially cylindrical member, a pluralitygo'f crushing bodies therein, means for feeding material to be crushed to one end of said cylindrical member, means for discharging material from the other end thereof, and driving means for rotating said 'cylindrical member, said member being formed on its inner Wall` with a plurality of annular portions inclined outwardly toward the feed end thereof, and with a plurality of annular portions intermediate said first-named annular portions and making a greater angle with the axis of the cylindrical member than said first-named portions.

5. In combination with a tubemill com-- prising a substantially cylindrical casing member provided with a plurality of crushing.. bodies in the interior thereof, with means for feeding material to be crushed to one end and means'for discharging `crushed material from the other end o said casing member, and with drivlng means for rotation thereof, a lining for said casing member comprising a plurality of annular sections adjacent one another, each of said sections being formed with an inner Wall portion inclinedoutwardly toward the feed end of the apparat-us and with .an abrupt wall portion making agreater angle with the axis of the cylindrical casing member than said first named wall portion. v

In testimony whereof I' have hereunto subscribed my name this 9th day of February 1924. v

CHARLES L. CARMAN.

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